The present invention relates to a method for controlling an advancing device on a machine for repetitive operations, especially for controlling the advancing speed of a slide carrying a cutting device of a cutting machine for cutting an elongated workpiece, such as a profile emanating at a predetermined speed from a profiling machine, an extrusion press, a straightening machine or the like, in sections of uniform length, in which the advancing workpiece hits an abutment, arranged on the slide in accordance with the length of the sections to which the elongated workpiece is to be cut, to thereby set the advancing device and subsequently thereto the cutting device or the like in motion. The present invention relates also to an arrangement for controlling such an advancing device and for carrying out the method.
Advancing devices are for instance known from the German Pat. No. 1,165,969, in which the drive of a separating slide or the like is controlled by means of an abutment, respectively a switching device, in such a manner that the slide is accelerated to the advancing speed of the workpiece for the separating operation. As drive for the slide may for instance serve a hydraulically operated cylinder and piston unit. The desired length of the sections to which the elongated workpiece is to be cut is adjusted with the mentioned abutment. When the workpiece hits the abutment a valve is operated over a linkage connected to the abutment for feeding pressure fluid into the cylinder and piston means forming the drive for the slide. In this known construction the workpiece actuates therefore the abutment and over the linkage connected thereto the valve member or control piston of the valve.
With increasing speed of the workpiece, which is desirable for increasing the output, the impining force of the workpiece against the abutment will increase, which will lead to a greater deflection of the abutment from its rest position. This known construction has, on the one hand, the disadvantage that thin and relatively weak profiles can be operated on only with a relative low speed, because otherwise they would buckle upon engagement with the abutment, which would detrimentally affect the exactness of the length of the sections to which the workpiece is to be cut. On the otherhand, by an increased deflection of the abutment at a higher speed of the workpiece the advancing device would be overcontrolled, if no corresponding provision on the regulating device would be provided, whereby again the exactness of the length of the sections to which a workpiece has to be cut would be reduced.